Tag: Size of molecules or ions

Cells need food materials which they can oxidise for energy or use to build up their cell structures. They also need salts and water, which play a part in chemical reactions in the cell. Finally, they need to get rid of substances such as carbon dioxide, which, if they accumulated in the cell, would upset some of the chemical reactions or even poison the cell. Substances may pass through the cell membrane either passively by diffusion or actively by some form of active transport.